Thank you so much for the quick responses Michael!

I suppose I should have been a little more clear in my choice of example to avoid any confusion. Going "straight up" in z is a particular subset of what I am trying to achieve (hence my edit about the snap options). To be more specific, the screen mode I am referring to could be summed up as : "the ability to freely move a control point along the X and Y axis of the camera plane, without affecting z (depth).

I have been using the Straight Snap as a workaround (both in create and edit modes, which is indeed a fantastic unified paradygm) but it is limited to the cases where points only need to be moved in a straight path in x, y or z, and very often I find myself wanting to hit something inbetween.

Anyways - these kind of UX subtleties are pretty hard to explain in words - I will try to make a quick gif asap to clarify what I mean :) Hope it can help!

(On a side note : the reason why I am hoping to be able to use MOI for such cases as opposed to regular polygon modeling environments is because of the simplicity and optimized nature of spline control points in MOI. I feel like I can nicely control a smooth curve in MOI and maintain its curvature easily, as opposed to the very destructive nature of polygon modeling. Also the surfacing options in MOI are much more user friendly than anything else out there - it's just a nice, fun program to use! :))